Seminconductor device and method of manufacturing the same

ABSTRACT

There is provided a method of manufacturing a semiconductor device, including forming a structure including a first layer containing Si and a metal oxide layer in contact with the first layer, the metal oxide layer having a dielectric constant higher than that of silicon oxide, and heating the structure in an atmosphere containing He and/or Ne.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Applications No. 2001-295367, filed Sep.27, 2001; and No. 2002-94149, filed Mar. 29, 2002, the entire contentsof both of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a semiconductor device and amethod of manufacturing the same.

[0004] 2. Description of the Related Art

[0005] In accordance with miniaturization of the silicon semiconductorintegrated circuit, the size of an MIS (Metal Insulator Semiconductor)transistor is rendered smaller and smaller. According to ITRS(International Technology Road map for Semiconductors), 2000 edition,the technology nodes of 60 nm require EOT (Equivalent Oxide Thickness),which is a thickness of the gate insulator converted into the thicknessof a silicon oxide film based on the dielectric constant, falling withina range of between 0.8 nm and 1.2 nm. However, if EOT is set to fallwithin the range noted above and a silicon oxide film or a siliconoxynitride film is used as a gate insulator, it is impossible tosuppress sufficiently the leak current. Therefore, it is necessary touse an insulating film with a high dielectric constant, i.e., a high-kfilm containing metal, as the gate insulator.

[0006] In recent years, vigorous research has been conducted on, forexample, Ta₂O₅, TiO₂, Al₂O₃, ZrO₂, HfO₂, Zr silicate (ZrSiO_(x)) and Hfsilicate (HfSiO_(x)) as a material of the next generation gate insulatorwith a high dielectric constant. Particularly, ZrO₂, HfO₂ and silicatesthereof are high in the thermodynamic stability on an Si substrate, havea high dielectric constant and a large band gap and, thus, areconsidered to be particularly hopeful as a material of the gateinsulator of the sub-1 nm generation.

[0007] However, the following problems are pointed out in respect of thethermal stability in the interface between the ternary insulator such asM—Si—O (M=Zr, Hf) and the Si substrate.

[0008] The first problem is derived from the situation that oxidizingspecies such as O₂ and H₂O have a relatively high diffusion rate withinthe particular insulator. If the oxidizing species have a high diffusionrate within the insulating film, traces of the oxidizing speciescontained in the atmosphere are readily migrated through the insulatingfilm during various heat treatment steps, with the result that a thickSiO₂ film is formed at the interface between the insulator and the Sisubstrate. The formation of the SiO₂ film lowers the dielectric constantof the gate insulator so as to increase EOT.

[0009] The second problem is brought about in the case where the partialpressure of the oxidizing species within the heat treating atmosphere islowered in an attempt to prevent the SiO₂ film from being formed.Specifically, if the structure of an insulating film/Si substrate issubjected to a heat treatment at a temperature not lower than 900° C.under UHV (Ultra High Vacuum) in which the partial pressure of theoxidizing species is lowered, it has been confirmed that a metalsilicide (MSi_(x)) is produced at the interface between the high-k filmand the Si substrate, which brings about degradation of the morphology.Incidentally, the particular reaction takes place not only at theinterface between the high-k film and the Si substrate but also at theinterface between the high-k film and a polycrystalline silicon(poly-Si) gate electrode or a polycrystalline silicon germanium(poly-SiGe) gate electrode.

[0010] As described above, in order to suppress the formation of an SiO₂film at the interface between the high-k film and the Si substrate, itis necessary to suppress the partial pressure of the oxidizing speciesto a low level in the atmosphere. However, if the partial pressure ofthe oxidizing species is excessively lowered, a silicide is formed.Therefore, in the case where an Si substrate having a high-k film formedthereon is subjected to a heat treatment step, it is necessary tocontrol the partial pressure of the oxidizing species in the atmosphereto fall within a prescribed range in order to suppress both formation ofan SiO₂ film and silicide.

[0011] However, the partial pressure range of the oxidizing species inwhich formation of an SiO₂ film and a silicide can be suppressed is verynarrow, which makes it very difficult to control the partial pressure ofthe oxidizing species to fall within the desired range. This raises aserious obstacle in applying a high-k film to the present semiconductorprocess, which includes many heat treatment steps at high temperaturessuch as an activation anneal.

BRIEF SUMMARY OF THE INVENTION

[0012] According to a first aspect of the present invention, there isprovided a method of manufacturing a semiconductor device, comprisingforming a structure including a first layer containing Si and a metaloxide layer in contact with the first layer, the metal oxide layer beinghigher in dielectric constant than silicon oxide, and heating thestructure in an atmosphere containing He and/or Ne.

[0013] According to a second aspect of the present invention, there isprovided a method of manufacturing a semiconductor device, comprisingforming a structure including a first layer containing Si and a metaloxide layer in contact with the first layer, the metal oxide layer beinghigher in dielectric constant than silicon oxide and at least one of thefirst layer and the metal oxide layer containing He and/or Ne, andheating the structure.

[0014] According to a third aspect of the present invention, there isprovided a semiconductor device, comprising a first layer containing Si,and a metal oxide layer in contact with the first layer, the metal oxidelayer being higher in dielectric constant than silicon oxide, and atleast one of the first layer and the metal oxide layer containing Heand/or Ne.

[0015] In each of the first and second aspects of the present invention,it is possible for the particular structure to further comprise a secondlayer. Also, the device according to the third aspect of the presentinvention may further comprise a second layer.

[0016] In each of the first to third aspects of the present invention,it is possible for the metal oxide layer to be a gate insulator. It ispossible for the first layer to include at least one of an Si underlyinglayer, a gate electrode and a sidewall insulating film. Also, it ispossible for the particular structure or the device to further compriseas the second layer at least one of, for example, an Si underlyinglayer, a gate electrode and a sidewall insulating film.

[0017] It is possible for the Si underlying layer to be, for example, anSi substrate or an Si substrate of an SOI substrate. It is possible forthat surface of the Si underlying layer which faces the metal oxidelayer to be oxidized. In other words, it is possible for the Siunderlying layer to comprise a silicon oxide film formed on the surfacethereof that faces the metal oxide layer.

[0018] It is possible for the first layer to be, for example, an Silayer or an SiGe layer. Alternatively, it is possible for the firstlayer to be an insulating layer containing Si such as a silicon oxidelayer or a silicon oxynitride layer.

[0019] Similarly, it is possible for the second layer to be, forexample, an Si layer or an SiGe layer. Alternatively, it is possible forthe second layer to be an insulating layer containing Si such as asilicon oxide layer or a silicon oxynitride layer.

[0020] The metal oxide layer has a dielectric constant higher than thatof silicon oxide. It is possible to use a metal oxide, a metaloxynitride or a silicate containing a metal, Si and oxygen as thematerial of the metal oxide layer satisfying the particular requirement.The material that can be used for forming the metal oxide layerincludes, for example, ZrO₂, HfO₂, BeO, MgO, SrO, BaO, Y₂O₃, CeO₂,Pr_(x)O_(y), Nd₂O₃, ThO₂, RuO₂, IrO₂, Al₂O₃, In₂O₃, ZrON, HfON,ZrSiO_(x), HfSiO_(x), ZrSiO_(x)N, and HfSiO_(x)N. It is possible for themetal oxide layer to be made of a single or a plurality of materials.Also, it is possible for the metal oxide layer to be of a single ormulti-layered structure.

[0021] In the first aspect of the present invention, it is possible forthe heat treatment of the structure to comprise heat treating thestructure in the atmosphere at an absolute temperature T of 650° C. orhigher. In this case, it is possible for the sum of the partial oxygenand water vapor pressures in the atmosphere, to be133×10^(11.703-18114/T) Pa or lower. Alternatively, it is possible forthis pressure to be 133×10^(8.903-18114/T) Pa or lower.

[0022] In the first and second aspects of the present invention, it ispossible for the formation of the structure to comprise forming a metaloxide layer on an Si underlying layer and depositing Si or SiGe on themetal oxide layer by a chemical vapor deposition using a silane gas asat least a part of a raw material gas so as to form the first layer. Inthis case, it is possible for the chemical vapor deposition to comprisedepositing Si or SiGe on the metal oxide layer with the temperature ofthe Si underlying layer set lower than 600° C., and further depositingSi or SiGe on the metal oxide layer by elevating the temperature of theSi underlying layer to 600° C. or higher.

[0023] It is possible for the method according to each of the first andsecond aspects of the present invention to further comprise patterningthe first layer and the metal oxide layer before heating the particularstructure so as to form a gate electrode and a gate insulator,respectively.

[0024] It is also possible for the method according to each of the firstand second aspects of the present invention to further compriseoxidizing the surface of at least one of the first and the second layersby using an oxidizing atmosphere containing He and/or Ne before heatingthe particular structure.

[0025] In each of the first and second aspects of the present invention,it is possible for at least one of the first layer, the second layer andthe metal oxide layer to contain He and/or Ne.

[0026] It is also possible for the method according to each of the firstand second aspects of the present invention to further comprisesupplying at least one of the first layer, the second layer and themetal oxide layer with He and/or Ne.

[0027] In the second aspect of the present invention, it is possible forthe heating of the particular structure to be carried out in anatmosphere containing He and/or Ne.

[0028] Further, in each of the first and second aspects of the presentinvention, it is possible for every heat treatments that is carried outat a temperature of 650° C. or higher after forming the particularstructure to be carried out in an atmosphere containing He and/or Ne.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0029]FIGS. 1A to 1F are cross sectional views schematically showing themethod of manufacturing a semiconductor device according to a firstembodiment of the present invention;

[0030]FIG. 2A is a graph showing the Zr3d spectra;

[0031]FIG. 2B is a graph showing the Si2p spectra;

[0032]FIG. 3 is a graph showing examples of the influences of thepartial pressure of the oxidizing species and the heat treatmenttemperature on the formation of an SiO₂ film and a silicide;

[0033]FIG. 4A is a view schematically showing the heat treatment carriedout in UHV or N₂ atmosphere;

[0034]FIG. 4B is a view schematically showing the heat treatment carriedout in a He atmosphere;

[0035]FIG. 5 is a graph showing the result of measurement by an in-situXPS carried out on a stacked structure of a ZrO₂ layer and a polysiliconlayer;

[0036]FIG. 6 is a graph showing the result of measurement by an in-situXPS carried out on a stacked structure of a ZrO₂ layer and anpolysilicon layer included in the MOS transistor;

[0037]FIG. 7A is a cross sectional view schematically showing theactivation annealing performed in UHV or N₂ atmosphere under the statethat the polysilicon layer does not contain He;

[0038]FIG. 7B is a cross sectional view schematically showing theactivation annealing performed in a He atmosphere under the state thatthe polysilicon layer contains He;

[0039]FIG. 8 is a cross sectional view schematically showing thestructure obtained by applying an oxidizing treatment to the structureshown in FIG. 1E; and

[0040]FIG. 9 is a graph showing the distribution of the Ne atomconcentration in a ZrO₂/SiO₂ stacked structure.

DETAILED DESCRIPTION OF THE INVENTION

[0041] Some embodiments of the present invention will now be describedin detail with reference to the accompanying drawings. Incidentally, theconstituting elements performing the same function are denoted by thesame reference numerals throughout the drawing for avoiding theoverlapping description.

[0042]FIGS. 1A to 1F are cross sectional views schematically showing themethod of manufacturing a semiconductor device according to a firstembodiment of the present invention. The first embodiment is directed toa method of manufacturing an MIS transistor by the method describedbelow.

[0043] First, a deep trench is formed in a surface region of a p-typesilicon single crystal substrate (or wafer) 11, as shown in FIG. 1A.Then, the trench is filled with a silicon oxide film 12 by a CVD(Chemical Vapor Deposition) method. The silicon oxide film 12 fillingthe trench plays the role of a device isolation region.

[0044] Next, a ZrO₂ layer 14 is formed on the substrate 11 as a high-kmetal oxide layer, as shown in FIG. 1B. Incidentally, the method offorming the ZrO₂ layer 14 including the pretreament will be describedherein later.

[0045] After formation of the ZrO₂ layer 14, a polysilicon layer 15 isformed on the ZrO₂ layer 14 by a CVD method, as shown in FIG. 1C,followed by forming a photoresist pattern 16 on the polysilicon layer15, as shown in FIG. 1D.

[0046] Then, the polysilicon layer 15 is patterned by RIE (Reactive IonEtching) with the photoresist pattern 16 used as a mask, followed bypatterning the ZrO₂ layer by RIE so as to obtain a gate electrode 14 anda gate insulator 14, as shown in FIG. 1E. After formation of the gateelectrode 15 and the gate insulator 14, an ion implantation of arsenicis carried out under an acceleration energy of 40 keV and with a dose of2×10¹⁵ cm⁻², followed by performing an activation anneal so as to formsimultaneously an n⁺-type gate electrode 15, an n⁺-type source region 17and an n⁺-type drain region 18 each having a high impurityconcentration.

[0047] Next, a silicon oxide film 19 is deposited in a thickness of 300nm by a CVD method on the entire surface, followed by patterning thesilicon oxide film 19 so as to form a sidewall insulating film and aninterlayer insulation film, as shown in FIG. 1F. Then, a photoresistpattern for forming contact holes is formed on the interlayer insulationfilm 19, followed by patterning the interlayer insulation film 19 by RIEwith the photoresist pattern used as a mask so as to form contact holesin the interlayer insulation film 19. Finally, an Al film is formed onthe entire surface by a sputtering method, followed by patterning the Alfilm so as to form a source electrode 110, a drain electrode 111 and asecond gate electrode 112, thereby finishing the manufacture of ann-type MOS transistor. Incidentally, FIGS. 1A to 1F are directed to aprocess of manufacturing an n-type MOS transistor. It should be noted inthis connection that a p-type MOS transistor can also be manufactured asabove, except that the conductivity type is rendered opposite to thatdescribed above.

[0048] The method of forming the ZrO₂ layer 14 will now be described.

[0049] Specifically, the structure shown in FIG. 1A is subjected to ahydrochloric acid/ozone treatment as a pretreatment so as to removeeffectively the contaminant from the surface of the silicon wafer 11. Asa result, a chemical oxide film having a thickness of about 1 nm isformed on the surface of the silicon wafer 11. Incidentally, it ispossible to apply a treatment with a dilute hydrofluoric acid afterformation of the chemical oxide film so as to decrease the EOT.

[0050] Next, the wafer 11 after the pretreatment is transferred into asputtering chamber. In the sputtering chamber, the ZrO₂ film 14 having athickness of about 2 nm is formed on the chemical oxide film by thesputtering method using a ZrO₂ target and an Ar/O₂ gas RF plasma (400 W)while maintaining the temperature of the wafer 11 at room temperature.

[0051] Then, a heat treatment is applied in a He and/or Ne atmosphere inorder to increase the density of the ZrO₂ layer 14 and to decrease thedefect therein. The heat treatment was carried out in a He atmosphere asan example. The heat treatment conditions in this case were as follows:Heat Treatment Conditions (He atmosphere): Background vacuum level: 133× 5.4 × 10⁻¹⁰ Pa He gas pressure: 133 Pa Sum of oxygen and water partialpressures 133 × 10⁻⁹ Pa in atmosphere: Substrate temperature: 920° C.Heat treatment time: 10 minutes

[0052] For comparison, heat treatments under conditions different fromthat described above were applied to two additional samples,respectively. One of these two samples was annealed in an N₂ atmosphereand the other was annealed in UHV, as shown below: Heat treatmentconditions (N₂ atmosphere): Background vacuum level: 133 × 5.4 × 10⁻¹⁰Pa N₂ gas pressure: 133 Pa Sum of oxygen and water vapor partialpressures 133 × 10⁻⁹ Pa in atmosphere: Substrate temperature: 920° C.Heat treatment time: 10 minutes Heat treatment conditions (UHV): Vacuumlevel: 133 × 10⁻⁹ Pa Substrate temperature: 920° C. Heat treatment time:10 minutes

[0053] The binding state in a stacked structure of the ZrO₂ layer 14 andthe SiO₂ film was examined by an in-situ XPS (in-situ X-rayphotoelectron spectroscopy) in respect of the samples after the heattreatments and the samples before the heat treatments. In measuring thebonding state, Mg K_(α) was used as the X-ray source, and the take-offangle of photoelectron was set at 45°. FIGS. 2A and 2B shows the result.

[0054]FIG. 2A is a graph showing the Zr3d spectra, and FIG. 2B is agraph showing the Si2p spectra. In the graph of each of FIGS. 2A and 2B,the binding energy is plotted on the horizontal axis and thephotoelectron intensity is plotted on the vertical axis.

[0055] As apparent from FIGS. 2A and 2B, a peak corresponding toZrSi_(x) is not included in the Zr3d spectrum and the Si2p spectrumobtained in respect of the sample before the heat treatment. Also, asshown in FIG. 2B, a low peak corresponding to SiO_(x) is included in theSi2p spectrum obtained in respect of the sample before the heattreatment.

[0056] As for the sample after the heat treatment in an N₂ atmosphere,as shown FIGS. 2A and 2B, a peak corresponding to ZrO₂ disappeared fromthe Zr3d spectrum and a peak corresponding to ZrSi_(x) appeared in theZr3d spectrum and the Si2p spectrum. Also, as for the sample after theheat treatment in N₂ atmosphere, as shown in FIG. 2B, a peakcorresponding to SiO_(x) disappeared from the Si2p spectrum and a peakcorresponding to SiN_(x) appeared.

[0057] As for the sample after the heat treatment in UHV, as shown inFIGS. 2A and 2B, a peak corresponding to ZrO₂ disappeared from the Zr3dspectrum and a peak corresponding to ZrSi_(x) appeared in the Zr3dspectrum and the Si2p spectrum. Also, as for the sample after the heattreatment under UHV, as shown in FIG. 2B, a peak corresponding toSiO_(x) was not included in the Si2p spectrum.

[0058] As described above, the ZrO₂ layer 14 disappeared in each of thecase where the heat treatment was carried out in an N₂ atmosphere andthe case where the heat treatment was carried out in UHV, and a ZrSi_(x)layer was formed in accordance with the disappearance of the ZrO₂ layer14. It is considered reasonable to understand that the particularsituation is brought about because the partial pressure of the oxidizingspecies is excessively low in the N₂ atmosphere and in UHV so as tobring about reactions represented by, for example, reaction formulas (1)and (2) given below:

SiO₂+Si→2SiO↑  (1)

ZrO₂+SiO↑+2.5Si→ZrSi₂+1.5SiO₂  (2)

[0059] Incidentally, a peak corresponding to SiN_(x) is included in theSi2p spectrum obtained in respect of the sample after the heat treatmentin an N₂ atmosphere. This is because that the SiO_(x) layer isdisappeared by the reaction (1) from the interface and the surface ofthe silicon substrate 11, from which the SiO_(x) layer is disappeared,is nitrided. Also, the ZrSi_(x) intensity of the sample after the heattreatment in an N₂ atmosphere and in UHV is lower than the ZrO_(x)intensity of the sample before the heat treatment. The particularsituation is considered to have been brought about because ZrSi_(x)grains produced by the reaction (2) were positioned not only on thesilicon substrate 11 but in the silicon substrate 11 and the amount ofZr atoms on the surface of the silicon substrate 11 was decreased. It isnoted that the state that ZrSi_(x) grains were embedded in the siliconsubstrate 11 from which the SiO_(x) layer had been disappeared wasobserved by cross section TEM (transmission electron microscope).

[0060] As described above, it was impossible to suppress ZrSi_(x) ineach of the case where the heat treatment was carried out in an N₂atmosphere and the case where the heat treatment was carried out in UHV.On the other hand, the Zr3d spectrum and the Si2p spectrum obtained inrespect of the sample after the heat treatment in a He atmosphere weresubstantially equal to the Zr3d spectrum and the Si2p spectrum obtainedin respect of the sample before the heat treatment, as apparent fromFIGS. 2A and 2B. In other words, formation of an SiO₂ film and asilicide is sufficiently suppressed in the sample subjected to the heattreatment in a He atmosphere.

[0061] Incidentally, the peak shape corresponding to ZrO₂ is sharperafter the heat treatment in a He atmosphere than that before the heattreatment and is slightly shifted toward a higher energy side. This isbecause the heat treatment in a He atmosphere increases a thermalstability of the structure of the ZrO₂ layer 14 and increases theinsulation properties so as to promote the charge-up caused by the X-rayirradiation. Also, the peak shape corresponding to SiO_(x) after theheat treatment in a He atmosphere is sharper than that before the heattreatment and is slightly shifted toward a higher energy side, thoughthe thickness of the SiO₂ film before the heat treatment remainsunchanged after the heat treatment in a He atmosphere. The particularsituation is brought about because the SiO₂ film is thermally stabilizedby the heat treatment in a He atmosphere.

[0062] As described above, in the case of utilizing a He and/or Neatmosphere, it is possible to suppress formation of an SiO₂ film and asilicide even if the heat treatment is carried out at a high temperatureexceeding 900° C.

[0063] Then, the influences of the oxidizing species partial pressure ina He and/or Ne atmosphere and the heat treatment temperature on theeffect of suppressing the formation of an SiO₂ film and a silicide werestudied.

[0064]FIG. 3 is a graph exemplifying the influences of the oxidizingspecies partial pressure and the heat treatment temperature on theformation of an SiO₂ film and a silicide. In the graph of FIG. 3, thevalue obtained by dividing 1000 by the heat treatment temperature T (K)is plotted on the horizontal axis, and the partial pressure of theoxidizing species (O₂ and H₂O) is plotted on the vertical axis.

[0065] The solid triangles shown in FIG. 3 denote the conditions for theheat treatment (the partial pressure of oxidizing species and the heattreatment temperature) performed in a He atmosphere of 133 Pa (1 Torr).Where the heat treatment was carried out in a He atmosphere, it waspossible to suppress the increase in the thickness of the SiO₂ film andthe formation of a silicide regardless of the partial pressure of theoxidizing species and the heat treatment temperature.

[0066] The solid line joining the solid circles in FIG. 3 denotes thereaction boundary of the oxidation-reduction reaction denoted byreaction formula (1) above, the oxidation-reduction reaction takingplace in the SiO₂/Si boundary in the case where the heat treatment iscarried out in an atmosphere that does not contain He. To be morespecific, in the region above the solid line, the reaction to form SiO₂is predominant, and the reaction to form an SiO gas is predominant inthe region below the solid line. Incidentally, the solid line can berepresented by an equation “P₀=133×10^(11.703-18114/T) Pa”, where P₀represents the partial pressure (Pa) of the oxidizing species, and Trepresents the heat treatment temperature (K).

[0067] Further, the broken line joining the solid squares in FIG. 3denotes the reaction boundary of the reduction reaction of the SiO₂layer that takes place in the ZrO₂/SiO₂/Si structure in the case wherethe heat treatment is carried out in an atmosphere that does not containHe. To be more specific, a silicide is not formed in the region abovethe broken line, and a silicide is formed in the region above the brokenline. Incidentally, the broken line can be represented by an equation“P₀=133×10^(8.903-18114/T) Pa”, where P₀ represents the partial pressure(Pa) of the oxidizing species, and T represents the heat treatmenttemperature (K).

[0068] In order to suppress the increase in the thickness of the SiO₂film and the formation of a silicide in the case where the heattreatment is carried out in an atmosphere that does not contain He, itis necessary to control the partial pressure of the oxidizing speciesand the heat treatment temperature to be positioned within a regionsandwiched between the solid line and the broken line in FIG. 3.However, the particular region is very small. In addition, it isimpossible to control the partial pressure and the heat treatmenttemperature completely uniformly. It follows that, where the heattreatment is carried out in an atmosphere that does not contain He, itis very difficult to suppress the increase in the thickness of the SiO₂film and the formation of a silicide.

[0069] On the other hand, where the heat treatment was carried out in aHe atmosphere, it was possible to suppress the increase in the thicknessof the SiO₂ film and the formation of a silicide even if the partialpressure of the oxidizing species and the heat treatment temperaturefailed to be positioned within the region sandwiched between the solidline and the broken line shown in FIG. 3, not to mention the case wherethe partial pressure of the oxidizing species and the heat treatmenttemperature were positioned within the particular region noted above. Inother words, the heat treatment in a He atmosphere permits markedlywidening the allowable ranges of the heat treatment temperature and thepartial pressure of the oxidizing species. It follows that theconditions for the heat treatment can be controlled easily.

[0070] Then, studied was the relationship between the effect ofsuppressing the increase in the thickness of the SiO₂ film and theformation of a silicide, which is produced by the use of a He and/or Neatmosphere, and the heat treatment temperature. It has been found as aresult of the measurement by an electron spin resonance (ESR) thatdangling bonds are formed at the SiO₂/Si interface, i.e., SiO isgenerated, in the case where the heat treatment temperature is 650° C.or higher. To be more specific, it has been clarified that the use ofthe He and/or Ne atmosphere is particularly effective in the case wherethe heat treatment temperature is 650° C. or higher. Incidentally, it isdesirable to carry out the heat treatment at a temperature at which theconstituting elements are unlikely to be deteriorated, though the upperlimit of the heat treatment temperature is not particularly specified.For example, where the metal oxide film is a ZrO₂ layer, it is desirableto carry out the heat treatment at a temperature of 1,200° C. or lowerat which the ZrO₂ layer is unlikely to be deteriorated, more desirablyat a temperatures of 1,050° C. or lower.

[0071] As described above, prominent effects can be produced by the useof the He and/or Ne atmosphere. The reason for the production of theparticular effect is considered to be, for example, as follows.

[0072]FIG. 4A schematically shows the heat treatment carried out in UHVor N₂ atmosphere, and FIG. 4B schematically shows the heat treatmentcarried out in a He atmosphere. Incidentally, the interface between theSi substrate and the ZrO₂ layer and the region in the vicinity of theinterface are depicted in each of FIGS. 4A and 4B. It should be notedthat a chemical oxide (SiO₂) film is formed on the surface of the Sisubstrate.

[0073] Where the heat treatment is carried out in UHV or N₂ atmosphere,an SiO gas is generated by the reaction (1) above in the Si/SiO₂/ZrO₂interface, as shown in FIG. 4A. In accordance with the progress of theSiO gas generation, SiO₂ layer in the interface decreases and ZrO₂layer, silicon substrate and SiO gas come into contact to one another soas to promote the generation of a silicide by the reaction (2) above.

[0074] It should be noted that the size and mass of each of the Hemolecule and the Ne molecule are smaller than those of the N₂ moleculeand, thus, the diffusion rate of each of the He molecule and the Nemolecule into the ZrO₂ layer is markedly higher than that of the N₂molecule. In other words, the N₂ molecules within the atmosphere areunlikely to be diffused into the ZrO₂ layer. On the other hand, the Hemolecules and the Ne molecules within the atmosphere are easily diffusedinto the ZrO₂ layer. In addition, it is possible for each of the Hemolecules and the Ne molecules to be present within the ZrO₂ layer in aconcentration higher than that of the N₂ molecules.

[0075] Therefore, where the heat treatment is carried out in the Heand/or Ne atmosphere, many SiO molecules generated in the Si/SiO₂/ZrO₂interface collide against the He molecules and the Ne molecules in thevicinity of the Si/SiO₂/ZrO₂ interface. As a result, the diffusion ofthe SiO molecules from the Si/SiO₂/ZrO₂ interface into the ZrO₂ layer issuppressed so as to suppress the reaction of reaction formula (2) toform a silicide.

[0076] It should also be noted that the He molecules and the Nemolecules arriving at the Si/SiO₂/ZrO₂ interface produce the quencheffect of suppressing the thermal vibration at the interface, e.g.,vibration of the Si—O bond. It follows that it is also possible tosuppress the generation of the SiO molecules by the reaction (1).

[0077] What should also be noted is that the He and/or Ne atmosphere inwhich the heat treatment is carried out is an inert atmosphere thatscarcely contains oxidizing species such as O₂ and H₂O. It follows thatthe degradation of the constituting element caused by, for example, theoxidation-reduction reaction is not generated by the use of the Heand/or Ne atmosphere.

[0078] As described above, it is considered possible to suppress theincrease in the thickness of the SiO₂ film and the formation of asilicide.

[0079] A second embodiment of present invention will now be described.

[0080] In the first embodiment, the structure shown in FIG. 1B wassubjected to a heat treatment in a He and/or Ne atmosphere so as toincrease the density of the ZrO₂ layer 14 and to decrease the defecttherein, as described above. In the second embodiment, however, the Heand/or Ne atmosphere is used as an atmosphere for carrying out anactivation anneal.

[0081] The second embodiment is substantially equal to the firstembodiment, except that the first and second embodiments differ fromeach other in the conditions for the activation anneal. Such being thesituation, only the differences from the first embodiment will bedescribed in respect of the second embodiment.

[0082] In the method according to the second embodiment, the structureshown in FIG. 1B is formed first by the method equal to that describedpreviously in conjunction with the first embodiment. Incidentally, aheat treatment for increasing the density of the ZrO₂ layer 14 and fordecreasing the defect is not carried out in the second embodiment. Then,the structures shown in FIGS. 1C and 1D are obtained in the ordermentioned by the methods equal to those described previously inconjunction with the first embodiment.

[0083] Next, the polysilicon layer 15 is patterned by RIE with thephotoresist pattern 16 used as a mask, followed by patterning the ZrO₂layer 14 by RIE. As a result, the gate electrode 15 and the gateinsulator 14 are obtained, as shown in FIG. 1E. Then, an ionimplantation of arsenic is carried out under an accelerating energy of,for example, 40 keV and at a dose of 2×10¹⁵ cm⁻², followed by applyingan activation anneal. In the second embodiment, the activation anneal iscarried out in the He and/or Ne atmosphere. The following descriptioncovers the case where the activation anneal is carried out in an Neatmosphere. The details of the conditions for the activation anneal areas given below. In this fashion, the n⁺-type gate electrode 15, then⁺-type source region 17 and the n⁺-type drain region 18, each having ahigh impurity concentration, are formed simultaneously. Further, thestructure shown in FIG. 1F is obtained by the method equal to thatdescribed previously in conjunction with the first embodiment, therebyfinishing the manufacture of an n-type MOS transistor. Heat TreatmentConditions (Ne atmosphere): Background vacuum level: 133 × 10⁻⁷ Pa Negas pressure: 1 atm Sum of oxygen and water vapor partial pressures 133× 10⁻⁶ Pa in atmosphere: Substrate temperature: 1,000° C. Heat treatmenttime: 10 seconds

[0084] The heat treatment temperature noted above and the partialpressure of the oxidizing species noted above are positioned in theregion below the broken line given in the graph of the heat treatmentconditions shown in FIG. 3. To be more specific, a silicide isgenerated, if the heat treatment is carried out within an atmospherethat does not contain He and/or Ne at the heat treatment temperaturenoted above and the partial pressure of the oxidizing species notedabove. In addition, the ZrO₂ layer 14 is covered with the thick gateelectrode 15 when the heat treatment is applied. It should be noted thatthe gate electrode 15 plays the role of preventing the oxidizing specieswithin the atmosphere from being diffused into the ZrO₂ layer 14.Therefore, where the heat treatment is carried out within an atmospherethat does not contain He and/or Ne at the heat treatment temperaturenoted above and the partial pressure of the oxidizing species notedabove, a silicide tends to be formed easily in the interface between thegate electrode 15 and the ZrO₂ layer 14.

[0085] On the other hand, where the heat treatment is carried out in anNe atmosphere as described above, it is possible to suppress formationof a silicide by the reasons equal to those described previously inconjunction with the first embodiment. It follows that it is possible tosuppress the increase in the roughness.

[0086] As described above, the oxidizing species are unlikely to bediffused into the ZrO₂ layer 14 under the state that the ZrO₂ layer 14is covered with the gate electrode 15. Therefore, an SiO₂ film isunlikely to be formed even where the partial pressure of the oxidizingspecies in the heat treatment atmosphere is relatively high. However, itis desirable for the sum of the oxygen partial pressure and the watervopor partial pressure within the He and/or Ne atmosphere to be133×10^(11.703-18114/T) Pa or lower, more desirably133×10^(8.903-18114/T) Pa or lower.

[0087] In order to suppress the diffusion of the oxidizing species intothe ZrO₂ layer 14, it is possible to form another cap film in place ofthe gate electrode 15. For example, it is possible to carry out the heattreatment within a He and/or Ne atmosphere under the state that thepolysilicon layer 15 is covered with a cap film, followed by removingthe cap film and subsequently forming the gate electrode 15.Incidentally, it is desirable for the cap film to have a thicknessfalling within a range of between 5 nm and 500 nm.

[0088] A third embodiment of present invention will now be described.

[0089] The method according to each of the first and second embodimentsmakes it possible to suppress the increase in the thickness of the SiO₂film and the formation of a silicide in applying an activation anneal ora heat treatment for increasing the density of the ZrO₂ layer 14 and fordecreasing the defect therein. However, the formation of a silicide arenot necessarily generated only during these heat treatments. Forexample, when the polysilicon layer 15 is formed by the CVD method usinga silane gas, the hydrogen generated by the thermal decomposition of thesilane gas reduces the surface of the ZrO₂ layer 14, with the resultthat a silicide is generated. The particular silicide formationdecreases the thickness of the ZrO₂ layer 14 and introduces defects intothe ZrO₂ layer 14 so as to increase the leak current. Also, since thepolysilicon layer 15 is thick, it is difficult to supply a sufficientlylarge amount of He and/or Ne into the ZrO₂ layer 14 when an activationanneal is applied in a He and/or Ne atmosphere. The method according tothe third embodiment is effective for dealing with the particularproblem.

[0090] The third embodiment is substantially equal to the firstembodiment, except that the third embodiment differs from the firstembodiment in the conditions for forming the polysilicon layer 15 andthat He is supplied to the polysilicon layer 15 in the third embodimentbefore the activation anneal. To be more specific, the structure shownin FIG. 1B is prepared first in the third embodiment by the method equalto that described previously in conjunction with the first embodiment.

[0091] Next, the polysilicon layer 15 is formed on the ZrO₂ layer 14 bythe CVD method using a silane gas. To be more specific, the substratetemperature is elevated to 500° C. in UHV of 8.0×133×10⁻¹⁰ Pa with thebackground vacuum level set at 133×5.4×10⁻¹⁰ Pa, followed by supplying asilane gas at a flow rate of 20 sccm. Incidentally, in the initialperiod of supplying a silane gas, the substrate temperature is set at500° C. and, then, the substrate temperature is elevated to 600° C.Also, the total pressure in this case is 1×133 Pa. The silane gas supplyis stopped 10 minutes after the start-up of the silane gas supply, andthe substrate temperature is lowered. If the polysilicon layer 15 isformed by the particular method, it is possible to suppress thegeneration of a silicide during formation of the polysilicon layer 15.

[0092]FIG. 5 is a graph showing the result of measurement by an in-situXPS carried out on a stacked structure of a ZrO₂ layer 14 and apolysilicon layer 15. Incidentally, Mg Kα was used as the X-ray source,and the take-off angle of photoelectron was set at 45°. Also, the graphof FIG. 5 shows the Zr3d spectrum. In the graph of FIG. 5, the bindingenergy is plotted on the horizontal axis, and the normalizedphotoelectron intensity is plotted on the vertical axis.

[0093] The curve of “As sputter” shown in FIG. 5 denotes the dataobtained in respect of the surface of the ZrO₂ layer 14 before formationof the polysilicon layer 15. Also, the curves of “SiH₄@500° C.” and“SiH₄@600° C.” denote the data obtained in the cases where the substratetemperature was set at 500° C. and 600° C., respectively, in forming thepolysilicon layer 15.

[0094] As shown in FIG. 5, ZrSi₂ is generated in the case where thesubstrate temperature is set at 600° C. in forming the polysilicon layer15. It should be noted in this connection that, where the substratetemperature is equal to or higher than 600° C., hydrogen, which is oneof the decomposed products of the silane gas, reduces ZrO₂ and, at thesame time, a reaction to form a silicide is carried out between SiH₂,which is the other decomposition product of the silane gas, and thereduced product of ZrO₂. On the other hand, where the substratetemperature is set at 500° C. in forming the polysilicon layer 15, ZrSi₂is not formed. It follows that it is possible to suppress the formationof a silicide if polysilicon is deposited with the substrate temperatureset lower than 600° C.

[0095] Incidentally, a silicide is formed in forming the polysiliconlayer 15 in only the poly-Si/ZrO₂ interface. Also, in view of thedepositing rate, it is advantageous to form the polysilicon layer 14with the substrate set at a high temperature. Therefore, it is desirableto cover the ZrO₂ layer 14 with polysilicon in the initial stage offorming the polysilicon layer 15 with the substrate temperature setlower than 600° C., followed by further depositing polysilicon byelevating the substrate temperature to 600° C. or higher.

[0096] After the structure shown in FIG. 1C is obtained as above, thestructure shown in FIG. 1D is obtained by the method equal to thatdescribed previously in conjunction with the first embodiment. Then, thepolysilicon layer 15 and the ZrO₂ layer 14 are patterned by the methodequal to that described previously in conjunction with the firstembodiment.

[0097] Next, He and/or Ne is introduced into the polysilicon layer 15 bymeans of an ion implantation. The following description covers the casewhere He is introduced into the polysilicon layer 15 by means of an ionimplantation under an accelerating energy of 40 keV and with a dose of2×10¹⁵ cm⁻². Incidentally, if the acceleration energy is increased, itis possible to introduce He and/or Ne into not only the polysiliconlayer but also the ZrO₂ layer 14 by the ion implantation.

[0098] After the ion implantation for introducing He and/or Ne into thepolysilicon layer 15, an ion implantation of arsenic and the activationanneal are carried out by the method similar to that describedpreviously in conjunction with the first embodiment. Since He iscontained in the polysilicon layer 15 as described above, it is possibleto supply a sufficiently large amount of He molecules from thepolysilicon layer 15 into the ZrO₂ layer 14. It follows that it ispossible to suppress the silicide formation by the reaction (2), etc. atthe poly-Si/ZrO₂ interface.

[0099] After the structure shown in FIG. 1E is obtained as describedabove, the structure shown in FIG. 1F is obtained by the method equal tothat described previously in conjunction with the first embodiment,thereby finishing the manufacture of an n-type MOS transistor.

[0100] In the method described above, an ion implantation is utilizedfor supplying He and/or Ne into the polysilicon layer 15. However, it isalso possible to utilize another method. For example, it is possible togenerate a He and/or Ne gas plasma by a capacitive coupling discharge oran ECR (electron cyclotron resonance) discharge and to supply He intothe polysilicon layer 15 by utilizing the gas plasma thus generated. Inthe case of using the He gas plasma, the electron temperature is 5 eV ina region having a high electron density, and the sheath voltage fordetermining the energy of the ion is about 15 eV. Therefore, if thesubstrate is disposed within such a region, it is possible to irradiatethe polysilicon layer 15 with ions having a high energy of about 15 eV.

[0101] A fourth embodiment of the present invention will now bedescribed.

[0102] In the third embodiment, the polysilicon layer 15 containing Heand/or Ne is obtained by supplying He and/or Ne into the polysiliconlayer 15. In the fourth embodiment, however, the polysilicon layer 15containing He and/or Ne is obtained by forming the polysilicon layer 15within an atmosphere containing He and/or Ne.

[0103] In the fourth embodiment, the structure shown in FIG. 1B isobtained first by the method equal to that described previously inconjunction with the first embodiment.

[0104] Next, the polysilicon layer 15 containing He and/or Ne is formedon the ZrO₂ layer 14 by the CVD method using a silane gas. For example,the substrate temperature is elevated to 500° C. while allowing a He gasto flow at a flow rate of 1 slm with the background vacuum level set at133×5.4×10⁻¹⁰ Pa. The pressure of the He atmosphere is 10×133 Pa. Then,a silane gas is supplied at a flow rate of 20 sccm, and a He gas issupplied at a flow rate of 120 sccm. Incidentally, the total pressure inthis case is 3×133 Pa. The supply of the SiH₄ gas is stopped 10 minutesafter start-up of the supply of the SiH₄/He mixture gas, followed bylowering the substrate temperature and subsequently stopping the He gassupply so as to obtain the polysilicon layer 15 containing He.

[0105] Then, the structure shown in FIG. 1D is obtained by the samemethod as that described previously in conjunction with the firstembodiment, followed by patterning the polysilicon layer 15 and the ZrO₂layer 14 by the same method as that described previously in conjunctionwith the first embodiment.

[0106] Further, the arsenic ion implantation and the activation annealin an atmosphere containing He and/or Ne are carried out by the methodsequal to those described previously in conjunction with the firstembodiment. The activation anneal is carried out under, for example, theconditions given below: Heat Treatment Conditions (He atmosphere):Background vacuum level: 5.4 × 133 × 10⁻¹⁰ Pa He gas pressure: 1 × 133Pa Substrate temperature: 920° C. Heat treatment time: 10 minutes

[0107] After the structure shown in FIG. 1E is obtained in this fashion,the structure shown in FIG. 1F is obtained by the same method as thatdescribed previously in conjunction with the first embodiment.

[0108]FIG. 6 is a graph showing the result of measurement by an in-situXPS carried out on a stacked structure of a ZrO₂ layer 14 and apolysilicon layer included in the MOS transistor obtained by the methoddescribed above. In performing the measurement, Mg Kα was used as theX-ray source, and the take-off angle of photoelectron was set at 45°.Also, the graph of FIG. 6 shows the Zr3d spectra. In the graph of FIG.6, the binding energy is plotted on the horizontal axis, and thenormalized photoelectron intensity is plotted on the vertical axis.

[0109] The curve of “(UHV→SiH₄/He)@500° C.+He@920° C.” shown in FIG. 6denotes the data obtained in the case where the formation of thepolysilicon layer 15 and the activation anneal were carried out underthe conditions given above. On the other hand, the curve of“(UHC→SiH₄)@500° C.+He@920° C.” shown in FIG. 6 denotes the dataobtained in the case where the formation of the polysilicon layer 15 andthe activation anneal were carried out under the same conditions aboveexcept that a He gas was not added on forming the polysilicon layer 15.Further, the curve “As-sputter” shown in FIG. 6 denotes the dataobtained in respect of the surface of the ZrO₂ layer 14 before formationof the polysilicon layer 15.

[0110] As shown in FIG. 6, a silicide was formed in the case whereformation of the polysilicon layer 15 was not carried out in thepresence of a He gas. It should be noted in this connection that thepolysilicon layer 15 was thick, and the pressure of the He atmospherewas low in performing the activation anneal, with the result that asufficiently large amount of the He molecules was not supplied into theZrO₂ layer 14. On the other hand, it is possible to supply asufficiently large amount of the He molecules into the ZrO₂ layer 14, ifHe is contained in the polysilicon layer 15 during the activationanneal, so as to make it possible to suppress the formation of asilicide.

[0111] The effect described above can be generated in the case where thepolysilicon layer 15 contains He in the applying the activation anneal.The reason for the generation of the particular effect is considered tobe as follows.

[0112]FIG. 7A schematically shows the activation anneal carried outwithin UHV or N₂ atmosphere under the state that the polysilicon layer15 does not contain He. On the other hand, FIG. 7B schematically showsthe activation anneal carried out within a He atmosphere under the statethat the polysilicon layer 15 contains He. Incidentally, the interfacebetween the Si substrate and the ZrO₂ layer, the interface between theZrO₂ layer and the polysilicon layer, and the regions in the vicinitythereof are depicted in FIGS. 7A and 7B. It should also be noted that achemical oxide (SiO₂) film is formed on the surface of the Si substrate.

[0113] Where the activation anneal is carried out within UHV or N₂atmosphere, an SiO gas is generated by the reaction (1) at theSi/SiO₂/ZrO₂ interface, as shown in FIG. 7A. The SiO gas is diffusedinto the ZrO₂ layer so as to form a silicide by the reaction (2) in, forexample, the poly-Si/ZrO₂ interface.

[0114] On the other hand, if the activation anneal is carried out withina He atmosphere and if the polysilicon layer 15 contains He before theactivation anneal, a sufficiently large amount of He molecules issupplied into the ZrO₂ layer, as shown in FIG. 7B. As a result, many SiOmolecules generated at the Si/SiO₂/ZrO₂ interface collide against the Hemolecules in the vicinity of the interface. It follows that it ispossible to suppress formation of a silicide in, for example, theSi/SiO₂/ZrO₂ interface and the poly-Si/ZrO₂ interface as describedpreviously with reference to FIG. 4B.

[0115] A fifth embodiment of the present invention will now bedescribed.

[0116] In each of the third and fourth embodiments described above, Heand/or Ne is supplied to the polysilicon film 15 before the activationanneal, or the polysilicon film 15 containing He and/or Ne is formedbefore the activation anneal. In the fifth embodiment, however, Heand/or Ne is supplied to the surface region of the substrate 11.

[0117] In the fifth embodiment, the structure shown in FIG. 1B isobtained first by the method equal to that described previously inconjunction with the first embodiment.

[0118] Next, the structure shown in FIG. 1B is subjected to ahydrochloric acid/ozone treatment as a pretreatment so as to removeeffectively the contaminant from the surface of the silicon wafer 11. Asa result, a chemical oxide film having a thickness of about 1 nm isformed on the surface of the silicon wafer 11. Incidentally, it ispossible to apply a dilute hydrofluoric acid treatment after formationof the chemical oxide film so as to decrease the EOT.

[0119] Next, the wafer 11 after the pretreatment is transferred into asputtering chamber. In the sputtering chamber, He and/or Ne is suppliedinto the surface region of the silicon wafer 11 by using He and/or Negas plasma. For example, the surface of the silicon wafer 11 isirradiated with an Ne gas RF plasma while maintaining the temperature ofthe wafer 11 at room temperature, with the result that Ne is suppliedinto the surface region of the silicon wafer 11. Then, the ZrO₂ layer 14having a thickness of about 2 nm is formed on the chemical oxide film bythe sputtering method using a ZrO₂ target and an Ne/O₂ gas RF plasma(400 W). In the structure shown in FIG. 1B thus obtained, Ne iscontained in a high concentration in the ZrO₂ layer, the Si/SiO₂/ZrO₂interface, and the regions in the vicinity thereof.

[0120] Further, the structures shown in FIGS. 1C to 1F are successivelyobtained by the methods equal to those described previously inconjunction with the first embodiment, thereby finishing the manufactureof an n-type MOS transistor.

[0121] As described above, the method of the fifth embodiment also makesit possible to suppress the formation of a silicide at, for example, theSi/SiO₂/ZrO₂ interface and the poly-Si/ZrO₂ interface like the methodaccording to each of the third and fourth embodiments.

[0122] A sixth embodiment of the present invention will now bedescribed.

[0123] In the sixth embodiment, He and/or Ne is supplied to the ZrO₂layer before the activation anneal. The method of the sixth embodimentalso makes it possible to suppress the formation of a silicide at, forexample, the Si/SiO₂/ZrO₂ interface and the poly-Si/ZrO₂ interface likethe method according to each of the third to fifth embodiments.

[0124] In order to supply He and/or Ne into the ZrO₂ layer before theactivation anneal, it is possible to utilize, for example, a He plasmaor an Ne plasma. In this case, however, it is desirable to use a plasmahaving a sufficiently low electron temperature in order to prevent, forexample, the substrate from being damaged. For example, where an Neplasma is generated by a capacitive coupling discharge, an inductivecoupling discharge or an ECR discharge, the electron temperature in anNe plasma region having a high electron density is 5 eV and the sheathvoltage, which determines the energy of the ions irradiating thesubstrate, is about 15 eV. If the substrate is irradiated with ionshaving a high energy of about 15 eV, the substrate is damaged. On theother hand, in a region having an electron temperature of 1 eV or lower,which is sufficiently apart from the Ne plasma region having a highelectron density, the sheath voltage is about 3 eV. Therefore, if thesubstrate is arranged in the region having a low electron temperature,it is possible to supply Ne to the ZrO₂ layer without damaging thesubstrate.

[0125] In order to supply He and/or Ne to the ZrO₂ layer 14 before theactivation anneal, it is possible to utilize the ion implantation of Heor Ne, or an annealing treatment in an atmosphere containing He and/orNe. It should be noted, however, that, in the case of utilizing the ionimplantation, it is desirable to set the accelerating energy at a lowlevel in order to suppress the damage done to the substrate. Also, inthe case of utilizing the ion implantation, it is desirable to repairthe defect generated by the ion implantation by a post-annealingtreatment.

[0126] A seventh embodiment of the present invention will now bedescribed.

[0127] In the seventh embodiment, the sidewall insulating film 19containing He and/or Ne is formed first, followed by carrying out anactivation anneal. To be more specific, in the seventh embodiment, thestructure shown in FIG. 1B is obtained first by the method equal to thatdescribed previously in conjunction with the first embodiment.Incidentally, in the seventh embodiment, the heat treatment forincreasing the density of the ZrO₂ layer 14 and for decreasing thedefect is not carried out. Then, the structures shown in FIGS. 1C and 1Dare obtained successively by the methods equal to those describedpreviously in conjunction with the first embodiment.

[0128] Next, the polysilicon layer 15 is patterned by the etching usingthe photoresist pattern 16 as a mask and a plasma of HCl/Cl₂/O₂,followed by patterning the ZrO₂ layer 14 by RIE, thereby obtaining thegate electrode 15 and the gate insulator 14 as shown in FIG. 1E.Further, an arsenic ion implantation is carried out under, for example,an accelerating energy of 40 keV and with a dose of 2×10¹⁵ cm⁻².Incidentally, in the seventh embodiment, the activation anneal is notcarried out in this stage and is carried out later.

[0129] Next, the silicon oxide film 19 is deposited on the entiresurface in a thickness of 300 nm by the CVD method of a TEOS/O₃ system.In the seventh embodiment, He and/or Ne is added to the raw material gasused for forming the silicon oxide film 19. The following descriptioncovers the case where He is added to the raw material gas so as toobtain the silicon oxide film 19 containing He.

[0130] Further, the structure shown in FIG. 1F is obtained by the methodequal to that described previously in conjunction with the firstembodiment. In the seventh embodiment, the activation anneal is carriedout any time after formation of the silicon oxide film 19, therebyfinishing the manufacture of an n-type MOS transistor.

[0131] As described above, in the seventh embodiment, the sidewallinsulating film 19 or the insulating film 19 before patterned containsHe and/or Ne. Therefore, during the activation anneal, He and/or Ne issupplied from the sidewall insulating film or the insulating film 19before patterned into the ZrO₂ layer 14. It follows that the methodaccording to the seventh embodiment also permits suppressing theformation of a silicide. Incidentally, the SiO gas tends to be generatedduring the heat treatment from the contact portion between thepoly-Si/ZrO₂ interface and the SiO₂ layer.

[0132] A eighth embodiment of the present invention will now bedescribed.

[0133] In the eighth embodiment, a gate electrode having a roundish edgeis obtained by oxidizing the surface of the patterned polysilicon film15. Also, in the eighth embodiment, the oxidation is carried out in anatmosphere containing He and/or Ne. To be more specific, in the seventhembodiment, the structure shown in FIG. 1B is obtained by the methodequal to that described previously in conjunction with the firstembodiment. Incidentally, the heat treatment for increasing the densityof the ZrO₂ layer 14 and for decreasing the defect is not carried out inthe eighth embodiment. Further, the structures shown in FIGS. 1C and 1Dare obtained successively by the methods equal to those describedpreviously in conjunction with the first embodiment.

[0134] Next, the polysilicon layer 15 is patterned by the etching usingthe photoresist pattern 16 as a mask and a HBr series plasma, followedby patterning the ZrO₂ layer 14 by RIE, thereby obtaining the gateelectrode 15 and the gate insulator 14 as shown in FIG. 1E. Then, thesurface of the gate electrode 15 is oxidized in an atmosphere containingoxidizing species and He and/or Ne. Further, a heat treatment is carriedout at 800° C. for 30 seconds in an atmosphere of atmospheric pressurecontaining, for example, 10% of oxygen and 90% of He. As a result, anoxide film 20 is formed on the surface of the gate electrode 15, and theedge of the gate electrode 15 is rendered roundish, as shown in FIG. 8.Incidentally, during the heat treatment, an oxide film is also formed onthe surface of the substrate 11. A reference numeral 21 shown in FIG. 8denotes the oxide film formed on the surface of the substrate 11.

[0135] Next, an arsenic ion implantation and an activation anneal arecarried out by the methods equal to those described previously inconjunction with the first embodiment, thereby obtaining the structureshown in FIG. 1E. Further, the structure shown in FIG. 1F is obtained bythe method equal to that described previously in conjunction with thefirst embodiment, thereby finishing the manufacture of an n-type MOStransistor.

[0136] In the eighth embodiment, the surface of the gate insulator 14 isoxidized in an atmosphere containing He and/or Ne and, thus, the oxidefilm 20 before the activation anneal contains He and/or Ne. It followsthat it is possible to suppress the formation of a silicide, which isderived from the SiO generation from, for example, the contact positionbetween the poly-Si/ZrO₂ interface and the SiO₂ layer during theactivation anneal.

[0137] In the eighth embodiment described above, the oxide film 20containing He and/or Ne is formed by oxidizing the surface of the gateinsulator 14 in an atmosphere containing He and/or Ne. Alternatively,the oxide film 20 containing He and/or Ne can also be formed by anothermethod. For example, it is possible to form the oxide film 20 byoxidizing the surface of the gate insulator 14 in an atmosphere thatdoes not contain He and/or Ne, followed by exposing the oxide film 20 toa He and/or Ne plasma. In this case, it is desirable to use a plasmahaving a sufficiently low electron temperature in order to prevent thesubstrate from being damaged. For example, in the case where an Neplasma is generated by a capacitive coupling discharge, an inductivecoupling discharge or an ECR discharge, a region of the Ne plasma havinga high electron density has an electron temperature of 5 eV and a sheathvoltage of about 15 eV. If the substrate is irradiated with ions havinga high energy of about 15 eV, the substrate is damaged. On the otherhand, in a region having an electron temperature of 1 eV or lower, whichis sufficiently apart from the region of the Ne plasma having a highelectron density, the sheath voltage is about 3 eV. Therefore, if thesubstrate is arranged in the region having a low electron temperaturenoted above, it is possible to supply Ne into the oxide film 20 withoutdamaging, for example, the substrate.

[0138] In order to supply He and/or Ne into the oxide film 20 before theactivation anneal, it is possible to utilize a He or Ne ion implantationor an annealing treatment in an atmosphere containing He and/or Ne. Itshould be noted, however, that, in the case of utilizing the ionimplantation, it is desirable to set the accelerating energy at a lowlevel in order to suppress the damage done to the substrate. Also, inthe case of utilizing the ion implantation, it is desirable to repairthe defect generated by the ion implantation by a post-annealingtreatment.

[0139] In each of the first to eighth embodiments described above, it ispossible to use any of a He atmosphere, an Ne atmosphere and a mixedatmosphere of He and Ne as the atmosphere containing He and/or Ne. Itshould be noted, however, that the particular effect described above isrendered prominent in the case where the He partial pressure is renderedhigher than the Ne partial pressure in the atmosphere.

[0140] In each of the first to eighth embodiments of the presentinvention, it is possible to dilute the atmosphere containing He and/orNe with a nobel gas such as Ar, Xe or Kr. It is also possible for theatmosphere containing He and/or Ne to be diluted with an inert gas otherthan the rate gas. For example, it is possible to use a nitrogen gas,N₂, for diluting the atmosphere containing He and/or Ne. Further, it ispossible to dilute the atmosphere containing He and/or Ne with an activegas in the case of carrying out a heat treatment accompanied by achemical reaction.

[0141] Also, in the case where the atmosphere containing He and/or Ne isdiluted with another gas such as an inert gas, it is possible toincrease the total pressure without increasing the partial pressure ofHe or Ne within the atmosphere. Since He or Ne selectively permeates theZrO₂ layer as described above, it is possible to promote the permeationof He or Ne into the ZrO₂ layer in this case without increasing theamount of He or Ne used. Also, it is possible to use a high purity inertgas such as a high purity N₂ gas, which is available easily, fordiluting the atmosphere containing He and/or Ne. Therefore, if theatmosphere is diluted with such a high purity inert gas, it is possibleto suppress the impurity concentration in the atmosphere at a low leveleven in the case where the purity of the He gas or the Ne gas is low.

[0142] It is possible for the sum of the He partial pressure and the Nepartial pressure in the atmosphere during the heat treatment to be anyof a decompression, an atmospheric pressure, and a compression. It isdesirable for the sum of the He partial pressure and the Ne partialpressure to fall within a range of between 1.33 Pa and 101,0800 Pa, moredesirably between 133 Pa and 13,300 Pa in view of the purity.

[0143] In each of the first to eighth embodiments described above, ZrO₂is used as the material of the metal oxide layer. However, it is alsopossible to use other materials such as HfO₂ and the silicate thereof inplace of ZrO₂, with substantially the same effect. Also, in each of thefirst to eighth embodiments described above, the metal oxide layer 14was formed by the sputtering method. However, it is also possible toform the metal oxide layer by other methods. For example, it is possibleto obtain the effect described above even in the case of forming themetal oxide layer 14 by using the thermal CVD method, the ALCVD (AtomicLayer CVD) method, the vapor deposition method, the plasma CVD method orMOCVD (Metal-Organic CVD) method.

[0144] In each of the first to eighth embodiments described above,poly-Si is used as the material of the gate electrode 15. However, it isalso possible to use another material for forming the gate electrode 15.For example, it is also possible to suppress the formation of a silicideeven in the case of using another material containing Si atoms such aspoly-SiGe.

[0145] In each of the first to eighth embodiments described above, themetal oxide film 14 is patterned before the ion implantation. However,it is also possible to pattern the metal oxide layer 14 after the ionimplantation. Also, in each of the first to eighth embodiments describedabove, an activation anneal is applied to mainly the structure shown inFIG. 1E. However, it is also possible to apply the activation anneal toanother structure. For example, an activation anneal can be applied tothe structure shown in FIG. 1F.

[0146] The technologies according to the first to eighth embodiments canbe combined appropriately. Particularly, it is desirable to carry outall the heat treatments at high temperatures, which are carried outafter formation of the metal oxide layer 14, e.g., the heat treatmentseach carried out at a temperature of 650° C. or higher, within anatmosphere containing He and/or Ne.

[0147] As described above, the technology according to the first toeighth embodiments makes it possible to lower the roughness in, forexample, the interface between the metal oxide layer 14 and thesubstrate 11 so as to suppress the leak current at the interface. Itfollows that the technology according to the first to eighth embodimentsis useful in, particularly, the case where the semiconductor device ofthe MIS structure described above is applied to a memory, e.g., anonvolatile memory which is provided with a memory function by forming afloating gate in the metal oxide layer.

[0148] In the MOS transistor obtained by the method according to each ofthe first to eighth embodiments, it is possible for He and/or Ne toremain in, for example, the metal oxide layer 14 so as to provide anevidence supporting that the particular method has been utilized.

[0149]FIG. 9 is a graph showing the distribution of the Ne atomconcentration in the ZrO₂/SiO₂ stacked structure. The data shown in thegraph were obtained by applying a secondary ion mass spectrometry (SIMS)to the MOS transistor prepared by the method according to the secondembodiment. In the graph of FIG. 9, the sputtering cycle is plotted onthe horizontal axis, and the Ne ion intensity is plotted on the verticalaxis. The empty circles in the graph denote the data obtained by themeasurement before the activation anneal. On the other hand, the solidcircles in the graph denote the data obtained by the measurement afterthe activation anneal.

[0150] As shown in FIG. 9, before the activation anneal in the Neatmosphere, the Ne atom concentration in the ZrO₂/SiO₂ stacked structureis substantially equal to the Ne atom concentration in the Si substrate.In other words, the Ne atom concentration in each of the ZrO₂/SiO₂stacked structure and the Si substrate is substantially zero.

[0151] On the other hand, after the activation anneal under the Neatmosphere, the Ne atom concentration in the ZrO₂/SiO₂ stacked structureis markedly increased, though the Ne atom concentration in the Sisubstrate remains substantially unchanged. Also, the Ne atoms aredistributed substantially uniformly in the ZrO₂/SiO₂ stacked structure.It is possible to judge whether or not the particular method wasutilized for manufacturing the MOS transistor by examining, for example,the Ne atom distribution.

[0152] Incidentally, in the case of employing the He atmosphere duringthe heat treatment, it is possible to observe the He atom distributionsimilar to the Ne atom distribution. Also, where a mixed atmosphere ofHe and Ne is used during the heat treatment, it is possible to observethe He atom distribution similar to the Ne atom distribution and the Neatom distribution. It is also possible to observe the He atomdistribution similar to the Ne atom distribution and/or the Ne atomdistribution in also the case where any of the constituting elementbefore the heat treatment contains He and/or Ne.

[0153] It is advantageous in various points for the manufactured MOStransistor to comprise the metal oxide layer 14 and He and/or Necontained in the vicinity of the metal oxide layer 14.

[0154] For example, where the ZrO₂ layer 14 contains He and/or Ne, it ispossible to moderate the stress at the interface between the Sisubstrate 11 and the metal oxide layer 14 and the stress at theinterface between the gate electrode 15 and the metal oxide layer 14. Inaddition, He and/or Ne serves to suppress the thermal vibration of thebond. As a result, the charge in the film and the interfacial leveldensity are lowered in the metal oxide film 14 containing He and/or Ne.It follows that the metal oxide layer 14 has a high dielectric constant,and a leak current is unlikely to take place in the metal oxide layer14. As a matter of fact, the leak current was measured in respect of theMIS capacitor subjected to an activation anneal in a He atmosphere. Ithas been found that the leak current was lowered to less than one-tenthof the leak current in the case where the activation anneal was carriedout in an N₂ atmosphere. Further, where the metal oxide film 14 containsHe and/or Ne and a silicate such as ZrSiO_(x) or HfSiO_(x) is used asthe material thereof, migration of interstitial atoms during the heattreatments is prevented so as to suppress the generation of phaseseparation, micro-crystal, etc. This improves in-plane uniformity of,for example, dispersion of leak current.

[0155] It should also be noted that, where the gate electrode 15contains He and/or Ne, He and/or Ne is segregated in the grainboundaries of the poly-Si so as to suppress the diffusion of theimpurities such as hydrogen and boron. The same effect can be obtainedin the case where the substrate 11 contains He and/or Ne. In addition,the mobility is improved because the thermal conductivity is increased.Further, where the insulating film 19 contains He and/or Ne, it ispossible to prevent impurities such as boron and hydrogen in thepolysilicon layer from diffusing into the insulating film 19. In thiscase, it is also possible to suppress the diffusion of impurities suchas hydrogen and carbon from the insulating film 19 into otherconstituting elements.

[0156] It is desirable for the concentration of He and/or Ne in themetal oxide layer 14 to fall within a range of between 1×10¹⁷ atoms/cm³and 1×10²¹ atoms/cm³. Where the concentration of He and/or Ne fallswithin the range noted above, the construction of the metal oxide layer14 is not changed by the presence of He and/or Ne.

[0157] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the present invention in itsbroader aspects is not limited to the specific details andrepresentative embodiments shown and described herein. Accordingly,various modifications may be made without departing from the spirit orscope of the general inventive concept as defined by the appended claimsand their equivalents.

What is claimed is:
 1. A method of manufacturing a semiconductor device,comprising: forming a structure including a first layer containing Siand a metal oxide layer in contact with the first layer, the metal oxidelayer being higher in dielectric constant than silicon oxide; andheating the structure in an atmosphere containing He and/or Ne.
 2. Amethod according to claim 1, wherein the first layer includes an Siunderlying layer, and forming the structure comprises forming the metaloxide layer on the first layer.
 3. A method according to claim 2,wherein heating the structure comprises subjecting the structure to aheat treatment in the atmosphere at an absolute temperature T of 650° C.or higher, and the sum of oxygen partial pressure and water vaporpartial pressure in the atmosphere is 133×10^(11.703-18114/T) Pa orlower.
 4. A method according to claim 2, wherein heating the structurecomprises subjecting the structure to a heat treatment in the atmosphereat an absolute temperature T of 650° C. or higher, and the sum of oxygenpartial pressure and water vapor partial pressure in the atmosphere is133×10^(8.903-18114/T) Pa or lower.
 5. A method according to claim 2,wherein the structure further comprises a second layer, the first andsecond layers sandwiching the metal oxide layer, and the second layerbeing an Si layer or an SiGe layer.
 6. A method according to claim 1,wherein every heat treatment that is carried out at a temperature of650° C. or higher after forming the structure is carried out in anatmosphere containing He and/or Ne.
 7. A method of manufacturing asemiconductor device, comprising: forming a structure including a firstlayer containing Si and a metal oxide layer in contact with the firstlayer, the metal oxide layer being higher in dielectric constant thansilicon oxide and at least one of the first layer and the metal oxidelayer containing He and/or Ne; and heating the structure.
 8. A methodaccording to claim 7, wherein the first layer includes an Si underlyinglayer, and forming the structure comprises forming the metal oxide layeron the first layer.
 9. A method according to claim 8, wherein thestructure further comprises a second layer, the first and second layerssandwiching the metal oxide layer, and the second layer being an Silayer or an SiGe layer.
 10. A method according to claim 7, wherein thestructure further comprises an Si underlying layer, the Si underlyinglayer and the first layer sandwiching the metal oxide layer, and thefirst layer being an Si layer or an SiGe layer.
 11. A method accordingto claim 10, wherein forming the structure comprises: forming the metaloxide film on an Si underlying layer; and depositing Si or SiGe on themetal oxide layer by a chemical vapor deposition using a silane gas asat least a part of a raw material gas so as to form the first layer; andthe chemical vapor deposition comprises: depositing Si or SiGe on themetal oxide layer with a temperature of the Si underlying layer setlower than 600° C.; and further depositing Si or SiGe on the metal oxidelayer by elevating the temperature of the Si underlying layer to 600° C.or higher.
 12. A method according to claim 7, wherein the first layercontains He and/or Ne.
 13. A method according to claim 12, furthercomprising patterning the first layer and the metal oxide layer beforeheating the structure so as to form a gate electrode and a gateinsulator, respectively.
 14. A method according to claim 13, furthercomprising supplying the gate electrode with He and/or Ne before heatingthe structure.
 15. A method according to claim 13, further comprisingoxidizing a surface of the gate electrode by using an oxidizingatmosphere containing He and/or Ne.
 16. A method according to claim 7,wherein the structure further comprises an Si underlying layer and agate electrode, the metal oxide layer is a gate insulator interposedbetween the Si underlying layer and the gate electrode, and the firstlayer is a sidewall insulating film formed on a side surface of astacked structure of the gate insulator and the gate electrode.
 17. Amethod according to claim 7, wherein heating the structure is carriedout in an atmosphere containing He and/or Ne.
 18. A method according toclaim 7, wherein every heat treatment that is carried out at atemperature of 650° C. or higher after forming the structure is carriedout in an atmosphere containing He and/or Ne.
 19. A semiconductordevice, comprising: a first layer containing Si; and a metal oxide layerin contact with the first layer, the metal oxide layer being higher indielectric constant than silicon oxide, and at least one of the firstlayer and the metal oxide layer containing He and/or Ne.
 20. A deviceaccording to claim 19, wherein the metal oxide layer contains Zr and/orHf.
 21. A device according to claim 19, further comprising a gateelectrode formed on the metal oxide layer, the gate electrode and thefirst layer sandwiching the metal oxide layer, wherein the first layerincludes an Si underlying layer, and the metal oxide layer is a gateinsulator.
 22. A device according to claim 19, further comprising an Siunderlying layer, the Si underlying layer and the first layersandwiching the metal oxide layer, wherein the first layer is a gateelectrode, and the metal oxide layer is a gate insulator.
 23. A deviceaccording to claim 19, further comprising: an Si underlayer supportingthe metal oxide layer; and a gate electrode, the gate electrode and theSi underlying layer sandwiching the metal oxide layer, wherein the metaloxide layer is a gate insulator, and the first layer is a sidewallinsulating film formed on a side surface of a stacked structure of thegate insulator and the gate electrode.